Lightning arrester

ABSTRACT

Serially connected discharging gaps are shunted by resistors and capacitors and disposed between a characteristic element and a line terminal within a grounded housing. At least one shielding ring encloses each gap and includes a disc connected to one end of an electrode forming each gap.

United States Patent Nagai et al. Mar. 14, 1972 [54] LIGHTNING ARRESTER[72 Inventors: Nobuo Nagai; Shoji Tada; Katsu Ujita, all [56] CM ofAmagasaki, Japan UNITED STATES PATENTS Assignee= Minubishi DenkiKabushiki Kaisha, 3,259,781 7/1966 Person ..3l7/6l x y m y Japan3,087,094 4/1963 Nash ..317/7o Filed: 2 Plttman 3 l X [2!] Appl. No.:58,874 Primary Examiner-James D. Trammell Attorney-Robert E. Burns andEmmanuel J. Lobato Aug. 1, 1969 Japan ..44/60866 Sedan y connecteddlschargmg gaps are shunted by reunion June 19, 1970 Japan -.45/53281and capacitors and disposed between a charmerinic element and a lineterminal within a grounded housing. At least one [52] US. Cl ..3l7/68,315/36, 317/70 shielding ring encloses h gap and indudes a di connected[51] Int 9/06 to one end of an electrode forming each gap. [58]FieldofSearch ..3l7/70,61,68;3l3/DIG.5;

8Chims,4DrawingFiguns LIGHTNING ARRESTER BACKGROUND OF THE INVENTIONThis invention relates to improvements in a lightning arrester includingan arrester element disposed within a grounded housing.

There have been already known lightning arresters of the. type includingan arrester element disposed within a grounded housing filled with anelectrically negative gas such as sulfur hexafluoride (SF for thepurpose of safely effecting the maintenance and inspection thereof. Suchlightning arresters have included voltage dividing elements consistingof resistors and capacitors in order to uniformly distribute anyelectric surge across discharging gaps involved. The surface of thevoltage-dividing element is affected by a potential due to the groundedhousing to cause the equipotential lines to obliquely penetrated intothe surface of the element. This causes a decrease in voltage with whicha corona discharge is initiated and also a decrease in withstand-testvoltage required between the voltage-dividing element and the groundedhousing. Although the voltage-dividing element can increase inlongitudinal dimension to increase the withstand-test voltage requiredbetween the same and the grounded housing this measure is undesirable inthat the resulting lightning arrester increases in overall dimension.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention toprovide a new and improved lightning arrester increased inwithstand-test voltage required between a voltage-dividing elementinvolved and a grounded housing for the arrester while making itdifficult to cause any corona discharge along the surface of thevoltage-dividing element.

It is another object of the invention to provide a new and improvedlightning arrester including a minimum number of voltage-dividingelements for controlling the electric discharge characteristics thereof.

The invention accomplishes these objects by the provision of a lightningarrester comprising a grounded housing and an arrester element disposedin the grounded housing characterized by a plurality of shielding ringsfor encircling the arrester element.

The adjacent shielding rings may be preferably different from each otherin dimension of an electrical conductor forming the ring.

Advantageously at least one of a diameter of the electrical conductorforming the shielding ring and the outside diameter of the shieldingring may progressively decrease from the side of the application ofvoltage toward the grounded side.

BRIEF DESCRIPTION OF THE DRAWING The invention will become more readilyapparent from the following detailed description taken in conjunctionwith the accompanying drawing in which:

FIG. 1 is a schematic longitudinal sectional view of a lightningarrester constructed in accordance with the principles of the invention;and

FIGS. 2, 3 and 4 are views similar to FIG. 1 but illustrating differentmodifications of the invention.

Throughout the Figures like reference numerals designate thecorresponding or similar components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingand FIG. 1 in particular it is seen that an arrangement disclosed hereincomprises a grounded housing filled with any suitable electricallynegative gas high in electrically insulating property, for example,sulfer hexafluoride (SP a characteristic element 12 disposed on thebottom of the housing 10, and a discharging gap unit 14 disposed on thecharacteristic element 12. The characteristic element 12 comprises anonlinear resistor formed essentially of silicon carbide (SiC). Even ifhigh electric surges resulting from lightning strokes reach thecharacteristic element to cause flows of high current therethrough theelement is operative to limit a voltage across the associated lightningarrester to a low magnitude while decreasing a current continuouslyflowing from the associated source of electric power into the arresterafter the discharge of the surges to a magnitude sufficient to bereadily interrupted by the discharging gap unit 14. The discharging gapunit includes a plurality of discharging gaps interconnected in seriescircuit relationship. Each gap has connected thereacross a resistor 16and a capacitor 18 forming a voltage-dividing element for thedischarging gap unit. Both end gaps of the unit 14 are connectedrespectively to the characteristic element 12 and a line terminal 20extending through the surface of the grounded housing 10 andhermetically surrounded by an electric insulation 22 sealed through thattop surface.

The voltage-dividing element formed of the resistors and capacitors 16and 18 respectively is effective for uniformly distributing electricsurges resulting, for example, from lightning strokes across thedischarging gaps but the surface thereof are affected by a potential dueto the grounded housing 10 so that equipotential lines are obliquelypenetrated into the surface of the voltage-dividing element. This leadsto a decrease in a voltage with which a corona discharge is initiatedalong the surface of the voltage-dividing element and/or a decrease in awithstand-test voltage required between the voltage-dividing element16-18 and the grounded housing 10. If it is desired to increase thatwithstand-test voltage, the voltagedividing element should increase inlongitudinal dimension. This results in a disadvantageous increase inthe overall dimension of the lightning arrester.

According to one aspect of the invention, those disadvantages areeliminated by the use of a plurality of shielding rings disposed outsidethe voltage-dividing element and around the discharging gap unit andtherefore around an arrester element formed of the voltage-dividingelement and the discharging gap unit. More specifically, as shown inFIG. 1, a plurality of shielding rings 24 are disposed in axiallyaligned, spaced relationship outside and slightly spaced away from thevoltage-dividing element 16-18 while they encircle the discharging gapunit 14. The shielding rings 24 are of the same construction and thesame dimension. Each of the shielding rings 24 comprises a length ofcircular, electrically conductive pipe bent into a closed circle and anelectrically conductive disc 26 connected at the outer periphery to theinner periphery thereof in the central plane. The disc 26 is sandwichedon the central portion between each pair of adjacent electrodes formingthe discharge gaps except for both end discs 26 having the centralportions sandwiched between the line terminal 20 and the adjacentelectrode and between the characteristic element 12 and the adjacentelectrode respectively. Thus the disc 26 and therefore the shieldingring 24 is maintained at the same potential as the gap electrodeconnected thereto. In FIG. 1 the four discharging gaps and the fiveshielding rings 24 are shown so that each discharge gap is operativelycoupled to at least one shielding ring.

The shielding ring and disc 24 and 26 respectively permit theequipotential lines to be penerated substantially perpendicularly intothe surface of the voltage-dividing element 16-18 to establish adesirable electric field around that element. This makes it difficult tocause a corona discharge along the surface of the voltage-dividingelement 16-18 while much increasing a withstand-test voltage requiredbetween the voltage-dividing element and the grounded housing. Thisresults in a small-sized lightning arrester.

For lightning arresters including the shielding rings as above describedthe withstand-test voltage required between the shielding rings and thegrounded housing is one of the important factors for determining thecapability of the arrester. It has been found that the larger thediameter a (see FIG. 1) of the circular conductor or the metallic pipeforming the ring 24 the more the established electric field will bealleviated and therefore the higher the withstand-test voltage.

In the arrangement of FIG. 1 the diameter a of the rings pipe can notsufficiently increase because the rings 24 are axially close to oneanother. As a result it is required to increase a distance between thegrounded housing and each of the shielding rings 24 designated byreference character b" representing a minimum spacing therebetween, forthe purpose of increasing the withstand-test voltage requiredtherebetween. This inevitably leads to an increase in lateral dimensionof the arrester.

This increase in lateral dimension of the arrester can be avoided by anarrangement as shown in FIG. 2. As shown, a plurality of largershielding rings 24A formed of an electrically conductive pipe of largerdiameter a alternate smaller shielding rings 248 formed of a conductivepipe of smaller diameter. The rings 24A and B have the outside diametersof d and d respectively while they are substantially equal in insidediameter. In other respects the arrangement is identical to that shownin FIG. 1.

Since the alternating rings 24A are of a larger diameter a, thewithstand-test voltage required between the rings 24 and the groundedhousing 10 can be sufficiently high even for the housing small inlateral dimension. Further a voltage applied across each of thedischarging gaps can be controlled by varying the diameters of the pipesforming the rings with the magnitudes of the voltage-dividing resistorsand capacitors remaining unchanged. Therefore the resulting arrester ispossible to be improved in discharge characteristics.

FIG. 3 shows a modification of the arrangement illustrated in FIG. 2.The arrangement of FIG. 3 is different from that illustrated in FIG. 2only in that, in FIG. 3, the shielding rings 24A and B are embedded inany suitable electrically insulating material 28 such as an expoxideresin into a unitary structure. This measure causes an increase inwithstand voltage required between each pair of adjacent rings to permita further increase in diameter of the pipe for the larger ring 24A andtherefore a further increase in withstand-test voltage required betweenthe rings 24 and the housing 10.

FIG. 4 illustrates another modification of the invention. As shown inFIG. 4 the discharging gaps l4 alternate the characteristic elements 12and have operative coupled thereto the respective shielding rings 24 onefor each gap. The rings 24 are formed of electrically conductive pipesprogressively decreased in diameter from the upper side as viewed inFIG. 4 or the side of the application of voltage toward the lower sideor the grounded side. It is seen that the rings 24 have respec tiveoutside progressively decreased from the upper side to the lower sidewhile the inside diameters thereof remain substantially unchanged. Theshielding rings 24 each have the conductive disc 26 connected at theouter periphery to the upper end thereof and sandwiched on the centralportion between the associated electrode for gap and the adjacentcharacteristic element.

The shielding rings 24 as shown in FIG. 4 serve to progressivelydecrease the stray capacitances between the same and the groundedhousing 10 as the rings is near to the grounded side with the resultthat any electric surge isallowed to be more uniformly distributedacross the discharging gaps 14. Therefore the arrangement of FIG. 4 isadvantageous in that the discharge characteristics can be controlledwithout the necessity of increasing the number of the voltage-dividingelements.

If desired, only one of the pipe's diameter and the outside diameter ofthe ring may changed in the manner as above described.

What is claimed is:

l. A lightning arrester comprising a grounded housing, a plurality ofgap units serially disposed within said grounded housing and defininggaps between successive gap units, voltage-dividing meansinterconnecting said gap units and a shielding ring encircling anddisposed radially outwardly of each said gap unit, and meanselectrically connecting each said shielding ring with the respective gaunit.

2 A lightmng arrester as claimed in c arm 1 wherein the adjacentshielding rings are difierent from each other in diameter of anelectrical conductor forming the ring.

3. A lightning arrester as claimed in claim 1 wherein said shieldingrings are embedded in an electric insulation.

4. A lightning arrester as claimed in claim 1 wherein at least one of adiameter of an electrical conductor forming said shielding ring and theoutside diameter of the said shielding ring progressively decreases fromthe side of the application of voltage toward the grounded side.

5. A lightning arrestor as claimed in claim 1, wherein said shieldingrings are formed of tubular conductors.

6. A lightning arrestor as claimed in claim I, wherein each saidshielding ring comprises a toroidal member and said connecting meanscomprises a disc extending out from said gap unit and united at itsperiphery with said toroidal member.

7. A lightning arrestor as claimed in claim 6, wherein said disc istangential to said annular member.

8. A lightning arrestor as claimed in claim 1, wherein a resistor and acapacitor are connected in parallel with one another across each gap.

* t =t l

1. A lightning arrester comprising a grounded housing, a plurality ofgap units serially disposed within said grounded housing and defininggaps between successive gap units, voltagedividing means interconnectingsaid gap units and a shielding ring encircling and disposed radiallyoutwardly of each said gap unit, and means electrically connecting eachsaid shielding ring with the respective gap unit.
 2. A lightningarrester as claimed in claim 1 wherein the adjacent shielding rings aredifferent from each other in diameter of an electrical conductor formingthe ring.
 3. A lightning arrester as claimed in claim 1 wherein saidshielding rings are embedded in an electric insulation.
 4. A lightningarrester as claimed in claim 1 wherein at least one of a diameter of anelectrical conductor forming said shielding ring and the outsidediameter of the said shielding ring progressively decreases from theside of the application of voltage toward the grounded side.
 5. Alightning arrester as claimed in claim 1, wherein said shielding ringsare formed of tubular conductors.
 6. A lightning arrester as claimed inclaim 1, wherein each said shielding ring comprises a toroidal memberand said connecting means comprises a disc extending out from said gapunit and united at its periphery with said toroidal member.
 7. Alightning arrester as claimed in claim 6, wherein said disc istangential to said annular member.
 8. A lightning arrester as claimed inclaim 1, wherein a resistor and a capacitor are connected in parallelwith one another across each gap.